Absorption type heat exchanging apparatus which is now in practical use, such as absorption type heat pumps and absorption type refrigerators comprise an evaporation unit, an absorption unit, a condensation unit and a regeneration unit. The refrigerant/absorption liquid combination used in this apparatus is generally a water/LiBr or NH.sub.3 /water combination.
Water and NH.sub.3, which are refrigerants, have high values of the latent heat of evaporation, being preferable in that the circulating amount of liquid required for the same refrigerating power is relatively small. Since the absorption liquid is circulated between the regeneration and absorption units which have pressures approximately equal to the saturation pressures respectively corresponding to the evaporation temperature and condensation temperature of the refrigerant, it is transferred to the higher pressure side after having its pressure increased by a pump, while it is transferred to the lower pressure side through a throttle valve. The power required for circulation is rather low.
Recently, freon type refrigerant (for example, "Freon 22", and "Freon" is trade name of polyhalogenated hydrocarbons containing fluorine and chlorine) has been considered to be useful because of such advantages as safety and a reduction in the size of the apparatus. However, since freon is generally low in the latent heat of evaporation, the circulating amount is greater than in the case of water or NH.sub.3. Another difficulty is that if predetermined temperature difference is to be obtained, there is involved a greater difference between pressures at the evaporation and condensation temperatures than in the case of water being used. Thus, the power of the pump for transferring the absorption liquid (for example, a solution of Freon 22 in diethylene glycol dimethyl ether) from the lower pressure side to the higher pressure side increases, raising a problem that the advantage of the required power being lower than that of the compression type heat pump or refrigerator is lost.
The required theroetical pump power of the refrigerator with respect to the refrigerant/absorption liquid combinations mentioned above is shown in Table 1.
TABLE 1 ______________________________________ Refrigerant/ Freon 22/ absorption liquid Water/LiBr NH.sub.3 /water DEGDME ______________________________________ Evaporation pressure 1.0 550 590 (k Pa) Condensation pressure 7.33 1600 1570 (k Pa) Circulating amount of 71 117 974 solution per Rt (kg/Rt) Theoretical pump power 1 .times. 10.sup.-4 0.046 0.36 (kW/Rt) ______________________________________ (Note) 1 Rt: 1 refregeration ton DEGDME: diethylene glycol dimethyl ether
The calculations in Table 1 are made on the assumption that the condensation temperature of the refrigerant is 40.degree. C. and its evaporation temperature is 7.degree. C. Further, it is assumed that the regeneration unit outlet temperature of the refrigerant is 90.degree. C. and the absorption unit outlet temperature is 40.degree. C.
It is seen from Table 1 that the freon type refrigerant requires 3600 times and 8 times as much pump power as that required by water and NH.sub.3, respectively.